Automatic telephone system



April 7, 1925.

A. ANDERSEN ET AL AUTOMATIC TELEPHONE SYSTEM 2 Sheets-Sheet 1 Filed Dec. 23. 1920 film finder 'n-ZnfzZZzam a um April 7, 1925. v

' A. ANDERSEN ET AL AUTOMATIC TELEPHONE SYSTEM Filed Dec 23 1920 2 Sheets-Sheet i R Patented Apr. 7, 19 25.

UNITED srArEs PATIENT. OFFICE.

ALBERT mnnnszm AND WI LIAM A. enarm, or enr'caeo, rumors, assrenon 'ro aurom'rrc nmorarc counmr, or omcaeo, rumors, a conrona'non or ILLINOIS.

auroua'rrd 'mnnrnoim srs'mu.

Application tiled December 28, 1920. Serial ll'o. 432,818.,

ter have come intoextended use in depart-.

ment stores, manufacturing plants, and the like. It is well understood that in an installation of this kind the more exacting requirements of the subscribers render itnecessary to provide a number of features which are not needed in a public exchange. The present invention is concerned particularly with one of these features, a feature that is known as conference calling. This is an arrangement to enable an ofiicial of a company having a private automatic exchange, or P. A.. X., to communicate with a number of his employees at the same time instead of having to talk to each one individually. That is, a conference connection may be established which includes three or more telephone sets all connected to the same conversationalcircuit at the same time. Figs. 1 and 2, when arranged with Fig. 2 underneath Fig.1, show the invention.

Fig. 1 shows the usual type of automatic telephone-substation A having a line switch C of the well known plunger type individual thereto; This line switch in common with the line switches C, C and a plurality of similar line switches in the group are adapted to be controlled by a master switch D and have access to trunk lines leading to connector selector repeaters similar to those shown at H and H. 'The function of the master switch D, as is well known, is to maintain all idle line switches opposite an idle trunk line. The connector selector repeaters H and H are of the well known Sirowger vertical and rotary type and have the usual 100 contact sets arranged in ten rows or levels. The first eight levels are arranged for local trafiic within the branch exchange and when'working on these levels ANDERSEN the switch H and -similar switches have the function of ordinary connectors except on the conference number. This exception will be explained fully hereinafter. The two top levels, namely, the ninth and tenth, are reserved for trunk lines. On these levels the switch H has the flmction of an ordinary selector. That is, when raised to the ninth or tenth level the switch will operate automatically to select an idle trunk line. The trunk lines terminating in one level,

say the tenth, extend to another P. A. X.

and on this level the switch H has also the function of an automatic-impulse repeater.

The arrangement of .the different bank levels may be betternnderstood in the more detailed consideration of the situation in which the P. A. X.- is used. It is assumed that the concern using the P. A. X. has two factories or other establishments located a short distance apart in a city served by a public manual exchange. One of the factories is supplied with telephone service by the P. A. X. under discussion while the other factoryis supplied with telephone service by another private automatlc exchange of the same type. The tenth level of the selector connector repeaters in the P. A. X. at factory number 1 is reserved for private trunk lines extending to the P. A. X. at factory No. 2, while the ninth level is used fortrunk lines extending to a public manual exchange.

From this explanation the wiring of the banks of the switches H and H will be readily understood. The conductors terminating in the bank contacts 130-132, inclusive, lead to a local substation B, which is similar to the'one shown at A, and are of course multiplied into the several connector switches. The bank contacts 138-140, inclusive, are the terminals of a trunk line extending to the P. A. X. in factory No. 2, and are multiplied into the local connector switches and represented in the connector H by the contacts 280 282, inclusive. The

contacts 141143,'inclusive, are the termi-.

nals of a trunk line leading to the public manual exchange and are multiplied in the usual manner throughout the local connecwith each connector, before being joined to the multiple. These relays associated with the switch H are characterized in the drawings by the reference numerals 150 and 15,1 and relays 260 and 261 are associated with the switch H. The multiple conductors of the conference number terminate in a plun ger type line switch C which has access to the local connectors including the connectors H and H. A

-Having briefly described the apparatus in the system, a more detailed description of its operation will now be given. For this pur-' pose itwill be assumed that the subscriber at substation A desires to have a conference with a number of other subscribers. To do this he will call the regular local number of the first subscriber desired in the conference prefixing the conference number (60). WVhen the receiver is removed at substation A a circuit is closed for the cnergization of the slow acting line relay of the individual line switch C over the following path: ground G, springs 35, line conductor 12, throughthe substation A. line conductor 11, springs 34, and thence through the wind ing of the line relay 15 to battery. The line relay 15 is energized over the above circuit and upon attracting its armature 18 completes a circuit for the pull down winding 16. The pull down winding, upon energlzmg, attracts the plunger arm and the cut off armature 26; the former bymeans of its plunger forcing the springs 3740, inclusive,'1nto engagement with their resting contacts, and the latter disconnecting the line conductors 11 and 12 from ground and battery respectively, by separating the contact springs 35 and 3 1. By the engagement of springs 37 and 40 with their resting contacts line conductors 11 and 12 are extended to the double wound line relay 60 at the connector H which, upon energizing, commaintain ground potential on the private. w

normal conductor 30 which extends to the multiply connected test contacts in the banks .of connectorswitches which have access to the line on which the subscriber at substa-.

tion A is located, thus guarding the line against intrusion in the ordinary manner. Another circuit closed by the operation of the line switch C is completed by the engagement of bank spring 39 with its resting contact. When these contacts are closed ground is extended in an obvious manner to the test contact associated with the selected trunk line in the test bank of the master switch D whereby the said master switch is operated and the plungers of all the other idle line switches in the group are advanced into association with an idle trunk line.

The foregoing operationshave occurred in response to the removal of the receiver at substation A and the line of the subscriber thereat has been extended by means of the line switch G into connection with an idle connector switch which is shown at H. The calling subscriber may now operate his calling device in accordance with the digits assigned in the conference number which, as

before mentioned, is the number 60. When,

the calling device is operated for the first energizes a corresponding number of times inresponse thereto. At each retraction of its armature 80 a circuit is completed ex tending from groundG, armature 80 and its back contact, armature 82 and the front contact, oif normalsprings 83 and 84, winding of the slow acting series relay 62, and the winding of the vertical magnet 71 to battery. The above is the circuit over which thefirst impulse is transmitted. At the first upward movement of the shaft the off normal springs are-shifted and the cir cuit is completed over a new path which is the same as the one previously traced except that it includes the off normal springs 83 and 85 and armature 87 of the series relay 62 and its front contact, (the series relay being now in operated position). By the operation of the vertical magnet 71 the wipers 120122, inclusive, are raised step by pletes the circuit of the slow acting releasesstep until they stand opposite the sixth level relay 61. Upon operating, the relay 61 at armature 81 places ground on the release trunk conductor extending back through working contact of spring 38 and the said spring and then through the holding winding 17 of the line switch C tobattery. The holding winding 17 is thereby energized in order to maintain the cut off armature 26 and the plunger arm 25 in an operated position. T is holding circuit is established beof bank contacts in which is located the set of contacts associated with the conference number 60. The slow acting series relay 62, which is energized in series with the vertical magnet, maintains its armature ,attracted throughout the vertical operation of the switch and at the end of the vertical movement deenergizes and transfers the operating circuit to the rotary magnet 72.

The calling subscriber may now operate his calling device in accordance with thesecond digit of the conference number. As before a series of interruptions is produced in the circuit of the line relay which deenergizes in response thereto a correspondin number of times. At each retraction of its armature 80 a circuit is completed for the rotary magnet 72 extendingpver the following path: ground G armature 80 and its back contact, armature 82 and its front contact, ofi' normal springs 83 and 85, armature 87-and its back contact, normally closed springs controlled byrelay 67, armature 114 and its back contact, and thence through the winding of the rotary magnet 72 to battery. The slow acting relay 68 is also energized in multiple with the above traced circuit thereby connecting the test wiper 121 to the test relay 67. The magnet 72 operates to rotate the wipers 120-122, inclusive, into engagement with the set of contacts associated with the conference number. Springs 94 and 77 are adjusted to be shifted into engagement with their working contacts 95 and 78 by a rotary cam on the switch when the switch shaft is rotated onto the conference number and then only. A. circuit is completed by the engagement of'springs 94 and 95 extending from ground G, through the winding of relay 65., springs 94 and 95, and then through the lower winding of the ring cut off relay 66 to batte Relays and 66 energize aver this circuit, relay 66 establishes a locking circuit for itself at armature 97 and at armature 96 and 98 and their front contacts prepares a repeating circuit. Upon the decuit may be traced from ground on release trunk conductor 98", armature 100 and its back contact, through the lower winding of the switching relay 69, back contact and armature 106, normally closed contact springs controlled by the relay 69, test wiper 121, test contact 126, and thence through the winding of relay 151 to battery. Relays 151 and 69 operate over this circuit. Relay 69 establishes a locking circuit for itself at armature 112 and its front contact, opens the rotary magnet/circuit at armature 114; and completes the operating circuit for the line relay 175 of the line switch C; i

The conductor leading from each test contact of the conference number in the several connector switches terminates in a relay associated with each connector, the conductor leading from the test contact 126 terminating in the relay 151 associated with the connector H. It follows therefore, that even though relay 69 operates to place ground on the test-contact 126 this will not extend to the test contacts in any of the other switches.

son, probably the manager, will have the privilege of setting up a conference and hence only one conference can possibly be going on at the same time. 2 7

To proceed, relay175energizes over a circuit extending as follows: ground G springs 179, conductor 166, conductor 172, back contact and armature 153, bank contact 127, wiper 122, front contact and armature 115, armature 98, and its front contact, front contact and armature 83", and through the lower winding of the impedance coil 64, armature 93 and its front contact, front contact and armature 92, upper winding of the impedance coil 64, back contact and armature 105, front contact and armature 96, armature 111 and its front contact, wiper 120, bank contact 125, armature 152 and its back contact, conductor 170,'conductor 165, springs 178, and through the winding of the line relay 175 to battery. Upon energizing, relay 175 completes a circuit for pull down winding 1'76. The pull down winding 1'76, upon energizing, attracts the plunger arm 189, and the cut off armature 180. By the operation of the plunger arm the springs 185 498, inclusive, areforced into engagement with their working contacts and the line conductors 165 and 166 are extended to the line relay 190 of the connector H by the shifting of springs 185 and 188 into engagement with their working contacts. Re lay 190, upon energizing, completes a circuit of the slow acting release relay 191 which operates to establish a holding circuit by placing ground on the release trunk conductor 200 extending by way of workingcontact of spring 186 and the said 7 spring thro'ughthe holding winding 177 of the line switch C to battery. This ground also extends over conductor 163 to the wind ing of the slow acting relay 155 to battery which energizes and repares a circuit for the relay 156. *The re ay 156 does not energizer at this timebeing short circuited by the holding ground on conductor 163. Re lays 155 and 156 are of high resistance while the resistance R is of low resistance, therefore relay 155 upon opera-ting does not establish a locking circuit for itself at armature 176.

The subscriber at substation A may now operate his calling device in'accordance with the first digit of the local subscribers numrelay 190. Slow acting relay 68 is energized also by the operation of relay 60 and serves to remove the impedance coil 64 from across the trunk conductors while the dial impulses are being sent. The line relay 190 of the connector H operates in the usual When the subscribervat substation A operates his calling device for the next v:digit of his desired number relay 60 responds to the interruptions in its line circuit and repeats them to the line relay 1900f the connector H. Bela 190-at each retraction of its armature sen s an impulse of current to the rotary magnet 207 in multiple with the slow acting relay 198. The magnet 207 operates to'rotate the wipers 250-252, inclusive, into engagement with the set of contacts with which the desired called subscribers line is associated, which "it will be assumed, is the set of contacts 289291, inclusive, associated with the line of subscriber at substation B. Relay 198 operates to connect the test wiper 251 to the test relay 197. If the desired subscribers line be busy. at this time ground potential will be present on test contact 290 engaged by the test wi or 251. A circuit may then be traced extendmg from the said grounded test contact by way of test wiper 251, normally closed springs controlled by relay 199, armature 215 and its front'contact, armature 239 and its back contact, and thence through the winding of the test relay 197 to-battery. Upon energizing, relay 197 completes a locking circuit for itself at armature 216 and placesthe busy. tone onjthe calling subscribers line over a circuit extending from the busy machine T' by way of armature 218 and its front contact, normally closed contact springs-controlled by relay 198, bank contact engaged by the spring 188 and the said spring, conductor 166, conductor 172, back contact and armature 153, bank contact 127,. wiper 122, front contact and armature 115, armature 98 and its front contact, front contact and armature 83 from whence it flows over the line conductor 12 to the substation'A. This tone will notify the subscriber that for the time being his desired number is busy, and he will replace his receiver upon the switchhook initiating the release of the switches C, H and H in the usual manner However, it will be assumed in the present case that,the desired subscribers line was idle when connection thereto was attempted. Under these circumstances follow ng the deenergization of the slow acting relay 198 a circuit is completed extending from ground on the release trunk conductor 200, armature 216 and its back contact, through the lower winding of the switching relay 199, back contact and armature 215, normally closed springs controlled by relay 199,

-: tendin t and its front contact, opens the rotary magnet circuit at armature 226, and prepares the ringing circuit of the called subscriber at substation B which is now efi'ective exfrom the ungrounded pole of generator y way of backco'ntact'and armature 222, armature 229 and its front contact,

wiper 252, bank contact 291, conductor 169, over the line conductor, through the ringer and condenser of the substation B, line conductor, conductor 167, bank contact 289, wiper 250, front contact and armature 227, armature 221 and its back contact, and thence through the lower winding of the ring cut off relay 196 to battery. Relay 196 is so adjusted that it does not respond to alternating current and hence the ringing of the subscriber at substation B will coning subscriber at substation A may converse with the subscriber at substation B and inform him that a conference is to be held and the numbers of the subscribers desired in the conference, after which the subscriber at substation B will hang up his receiver thereby breaking the circuit of the back bridge relay 194. Upon the deenergization of relay 194 ground is removed for a short interval from the release trunk conductor 200 that is, during the interval that the slow acting relay 193 remains operated after the deenergization of relay 194. This operation breaks the circuit of the holding winding 177 of the line switch C, also the circuit of the slow acting relay 155 and atthe same time removes the short circuit around relay 156. The slow acting relay 156 energizes and prepares a circuit which is effective upon the energization of the line relay 175. Then 7 the holding winding deenergizes plunger arm 189 and cut off armature 180 resume the normal position. A circuit is thereupon completed for the line relay 175 which again energizes closing the circuit III of the pull down winding 17 6 and also placthe numbers of the parties desired. Then.

ing ground on conductor 164 extending by this last called subscriber hangs up his, reway of. armature 159 and its front contact, -ceiver ground is removed from the release conductor 171, normally closed springscontrunk 200 in a manner herelnbefore extrolled by relay 150, armature 157 and its plained and the relay similar to relay 150 front contact, and through the winding of associated with the connector used by the relay 150 to battery. Relay 150 energizes \subscriber at substation B is operated to thereby establishing a locking circuit for itself at armature 156 andat armatures 152 ference holding trunk.

and 153, opening the circuit to the line In the same manner 'the second called switch C and at the front contacts of these party will call another subscriber and in armatures extending theline conductors of turn be transferred onto the holding trunk.

I the substation A to the conference holding The last subscriber to be included in the trunk comprisingconductors 173*and 174. conference will have to call a special num- The line switch C and the connector H her as he will not have another subscriber will therefore release freeing the line of the to-call. This number is represented by the subscriber at substation B. bank contacts 135-137 inclusive, associated The subscriber at substation B will now w h connector H and is of coursemulll th u b f th ne t ubs riber de 'tipled throughout the local switches in the. sired in the conference. When the receiver t Usual manner. The last subscriber to be i v d t b t ti B th li it h called .will therefore operate his calling de- C? will operate to extend the line of that subscriber to an idle connector switch in a manner hereinbefore explained. When this occurs the line relay of the connector switch so seized will energize completing the circuit of the slow actin release relay which also energizes and esta lishes a holding circuit for the line switch C The subscriber at substation B will now operate his calling device in accordance with he digits of the conference number. The connector under his control is thereby stepped into engagementv with the setof back-contacts corresponding to 60. When this occurs the line switch C" associated with the conference sumed is the connector shown at H.

number will operate "as before to. connect with an idle connector which it will be as- The subscriber at substation B will thereupon operate his calling device .in accordance with the local number of the subscriber next desired in the conference. The connector H will therefore be operated into engagement with the set of bank contacts associated with the line of the desired subscriber. If this line, is busy a bu signal will be given to the callingtubscri er at substation B in the usual manner. However, it will be assumed in the present case that the line of this subscriber is idle when connection thereto is attempted. The connector H will now operate to intermittently supply ringing current to the line of the called subscriber until an answer. is obtained. When this occurs the ring out off relay 196 will energize and complete the circuit of the back bridge relay 194, which also energizes over the line circuit of the called subscriber. Upon energizing, relay 194 completes the circuit of the slow acting relay 193. Conversation may now be carried on between the subscriber at substation B and the second called subscriber. The calling subscriber will inform him that a conference is to be held and also vice in accordance with the number associated with the bank contacts 135-137, inclusive. Then the receiver is removed the line switch individual to this subscribers transfer the subscriber thereat onto the conline operates to connect with an. idle connector. der the control of its line relay toconne1t with the bank contacts similar to contacts 135-137, inclusive. The line .conductors leading from these contacts terminate directly in the holding trunk. Battery is placed through resistance on the private normal conductor-175. The test wiper similar to the test wiper 121 of the connector H upon finding battery will 'complete and the circuit of the switching relay similar to relay 69. This relay vwill then operate-to prepare the talking circuit. No ringing J current will be applied to the holdingtrunk bythis connector as the ring'cut off relay of the connector is immediately operated, a v path for direct current being effective This connector will be operated unthroughthe impedancecoil 64and similar coils of the operated switches. All the subscribers desired in the conference are now connected with the holding trunk and each is supplied talking battery by the line relay of the various associated switches.

\Vhen the conference is terminated each subscriber by replacing his receiver upon the switchhook will open the circuit of the. line relay of his associated connector switch thereb completing the release magnet circuit 0 each connector in the ordinary manner.

The explanation of the manner in which a trlmk connection to themain exchange is established may now be proceeded with. As before stated, the trunk lines extending to the main exchange terminate in the ninth level. It follows therefore, that in order to connect with one of these trunk lines the digit 9 must be called. The subscriber at substation A who desires to connect with the 1 ceiver and operate his calling device in accordance with the digit 9. When the receiver is removed the line switch C operates as before described to extend the associated line to a trunk line terminating in an idle selector-connector repeater. It will be assumed that: the switch H is idle and is selected for use, when connection is extended thereto the line and 'release relays 60.and 61 are energized as previously explained and with the same results. When the calling device is operated the switch wipers 120-122, inclusive, are raised etc by step by the vertical magnet 71 under t e control of the line relay 60 and are brought to rest opposite the ninth level, all in the manner previously explained. ;,When the wipers are raised to the ninth level the shaft controlled spring 74 is brought into engagement with"spring"73 by the operation of the shaft. This may be accomplished by any suitable cam arran ement. A convenient way is to mount t e spring assembly comp-rising springs 73-76,

inclusive, just above the top of the shaft so that the springs 74 and 76 will be actuated by the circular cup spring casing which is mounted on the upper extremity of the switch shaft. To proceed, the slow acting relay 62 is energized in series with the vertical magnet and at armature 86 and its front contact completes a circuit extending from groundf on release trunk conductor 98 by way of the shaft controlled springs 73 and 74, springs 78 armature 86 and its front contact, armature 77 and its back contact, and through the winding of the test relay 67. to battery. Upon energizing, relay 67 completes a locking circuit for itself at armature 100 and its front contact, and at armature 101 and its front contact prepares the rotary magnet circuit. Upon the termination of the vertical movement of the switch the slow acting relay 62 deenergizes and a circuit is thereby completed extending from ground on release trunk conductor 98 by way of the shaft controlled springs 73 and 74, springs 78, armature 86 and its back contact, armature 101 and its front contact, armature 114 and its back contact, and thence through the winding of the rotary magnet 72 to battery. Upon operating, 'magnet 72 steps the wipers 120-122, inclusive, into engagement with the first set of contacts in the ninth level and also breaks the looking circuit of the test relay 67 which deers 120-122, inclusive, is or is not busy. If busy, a ground potential will'be present on the test contact engaged by test wiper 121. A circuit is thereby completed extending from the said grounded test contact by way of' the test wiper 121, normally closed springs controlled by the relay 69, armature 106 and its front contact, armature 77 and its back contact, and through the winding of the test relay 67 to battery. Relay 67 again operates to close the rotary magnet circuit at armature 101 and establish a locking circuit for itself atarmature 100. Mag

net 72 operatesto rotate the switch wipers into engagement with the next set of confacts in the ninth-level and break the lock ing circuit of'relay 67. The alternate operation of relay 67 and magnet 72 will con tinue until an idle trunk line is found, which it will be assumed, is the trunk line terminat ing in the bank contacts 141-143, inclusive, the test contact 1420f which will be un grounded. Ground being no longer present on the test contact engaged by the wiper 121 no circuit will be competed for the test relay 67 Following the deenergization of the slow acting relay 68 a circuit is completed extending from ground 'on release trunk conductor 98, by way of armature 100 and its back contact, through the lower windin sistance R to battery. Relay 69 energizes over this circuit establishing a locking circuit for itself at armature 112 and at armatures 111 and 116 and their front contacts prepares a ringing circuit. Ringing current is automatically projected over the trunk line which terminates in bank contacts 141*143, inclusive, in the same manner as in the case of a called local line and the ring down drop or other signalling device at the manual switchboard is operated in the usual manner. When the operator plugs in to an swer the call the ring out of? relay 66 is operated, disconnects the ringing current, and completes the talkin connection. The connectlon to the desire local substation in the main exchangemay be completed .by the operator through the medium of any suitable means which need not be explained herein.

The operation of the selector connector repeater H when used for trunking to the second private automatic exchange is the same as in the case just described in so far as the selection of an idle trunk line-is concerned, but since the connection in the private automatic exchange must be completed automatically the circuits of the switch H are altered suitably in order to permit the switch to operate as a repeater for the purpose of repeating impulses over the selected trunk line. Since the trunk lines leading to the second private automatic exchange terleading to the P. A. X. number 2, where it m'inate in the tenth level the subscriber at substation A who desires to. connect thereto will remove his receiver and operate his calling device for the digit 0. When the receiver is removed the line switch C operates as before to connect with an idle selector con-- nector repater-II. When the digit 0 is sent to the'switch the line relay 60 operates in response thereto and controls the vertical movement of the switch in step ing to the tenth level. On the tenth vertical step of the shaft theshaft controlled springs 73 and 74, and 75 and76, are brought into engage ment. The switch H will operate as previously described to select an idle trunk line when the cam springs 94 and 95 were brought into engagement when the conference number .was called. The repeating circuit is thereby completed in the same manner as there described. The connection in the second private automatic exchange will therefore be completed in the usual man- Having fully ascertainedand described the 1- features of our invention, what we consider appended claims:

to be new and desire to have protectedby Letters Patent will be pointed out in the What I claim as my'invention is:

1. In a telephone system, calling and called lines, anautomatic connector switch. means whereby the subscriber on one of said calling lines may establish a. connection with one of said called lines by means of said switch,'a holding trunk, and means responsive to the restoration of the receiver at the called substation for transferring the connection of the calling line to the said holding trunk.

2. In a telephone system, calling and called lines, automatic switches, means whereby the subscriber on oneof said calling lines may establish a connection with one of said called lines through a series of said automatic switches, a holding trunk, and means responsive to --the restoration of the receiver at the called substation for releasing a part of said series of switches and transferring the calling line into connection with the sa1d holding trunk.

3. In a telephone system, calling and called lines, automatic switches, means whereby the subscriber on one of saidcalling lines may establish a connection with one of said called lines through -a series of said automatic switches, a holding trunk, and means responsive to the restoration of the receiver at the called substation for transferring the calling I line into connection with the said holding trunk.

4. In a telephone system, calling and called lines, an automatic connector switch, means whereby the subscriber on one of said calling lines may establish a talking connection with one of said called lines by way of the said automatic switch, means under the control of the said calling subscriber only for releasing said automatic switch, means whereby the said calling subscriber may establish a connection with another of said called lines by way of the said automatic switch, and means under the control of the second called subscriber for releasing said automatic switch.

5. In a telephone system, callingv and called lines, an automatic connector switch, means whereby the subscriber on one of said calling lines may establish a connection with one of said called lines by way of the said automatic switch, means under the control of the said calling subscriber only for relcasing'said automatic switch, means whereby the said calling subscriber may establish a connection with another of said called lines by way of the said automatic switch, and means underthe control of eitherthe releasing said automatic switch.

6. In a telephone system, calling and called l nes, automatic switches, a holding trunk, means whereby the subscriber on one of said calling lines may establish a connection with one of said. called lines through a series of said automatic switches, means whereby the subscriber on said called line may place the calling line into connection with the holding trunk and then call a second called line, and means under the control of the subscriber on the second called line for placing the first called line into connection with the said holding trunk.

7. In a telephone system, calling and called lines, a holding trunk, automatic switches, means whereby the subscriber on a calling -line may establish a connection with a called line through a series of automatic switches, means whereby the subscriber on the said called line may pass the connection to another called line, and means under the control of each called subscriber for placing the calling lines into connection with the said holding trunk.

8. In a telephone system, calling and called lines, an automatic switch, a'second automatic switch accessible through the banks of said first switch, multiple bank contacts in each of said switches individual to said called line, means whereby the subscriber on the calling line can operate said first switch to connect with the called line independent of said second switch, and whereby the said subscriber can establish ioo another connection with the called line by operating said switches successively.

9. In a telephone system, calling and called lines, an automatic switch, a second automatic switch, bank contacts in said first switch individual to said called line, a second 'set of bank contacts in said first switch individual to said second switch, a third set of bank contacts in said second switch individual to said called line, means including the first switch for connecting said lines by way of said first set of bank contacts and independent of the other sets, and means including both switches for connecting said lines by way of the second and third sets of bank contacts.

10. In a telephone system, line switches individual to the subscribers lines, connectors accessible to said line switches and having access to the subscribers lines, a special line switch having access to said connectors in common with the subscribers line switches, and a trunk line accessible to said connectors and terminating in said special line switch.

11. In a telephone system, line switches individual to the subscribers lines, connectors accessible to said line switches and having access to the subscribers lines, a special line switch having access to said connectorsline in common with the subscribers switches, a trunk line accessible to said connectors and terminating in said special line switch, sets of normal conductors constituting thev means by which the connectors are connectors operablesuccessively y difi'erent calling subscribers to establish connections with called lines, the subscriber on the called line in each connection being the calling subscriber who establishes the next connection, a common talking circuit, and means for switching each calling line into connection with said talking circuit when the subscriber on the associated called line hangs up preparatory to calling the next line.

13. In a telephone system, the method of establishing a conference'connection which consists in having each subscriber except the last call the next subscriber, and in hav- I ing each calling subscriber switched to a common talking circuit by the subscriber he has called. 14. In a telephone'system, the method of establishing a conference connection which consists in the establishment of a plurality of separate connections by a plurality of successively calling subscribers, and in sue cessively switching each calling subscribers line on to a common talking circuit;

, Signed by us at Chicago, Cook County, Illinois, this 10th day of December, 1920.

ALBERT ANDERSEN. WILLIAM A. CHAPIN. 

